1. Field of the Invention
This invention relates to a webbing retractor for use in a seatbelt system for protecting an occupant in an emergency of a vehicle such as a collision, and particularly to a webbing retractor wherein the webbing is forceably retracted in an emergency of the vehicle to closely hold the occupant at a seat.
2. Description of the Prior Art
In general, webbing retractors are constructed such that one end of the webbing is adapted to be wound up into a winding barrel by a biasing force, the webbing is surroundingly attached to the occupant by said biasing force when the webbing is fastened to the occupant, and such a cosideration is paid that, after the webbing is unfastened, most part of the webbing is wound up into the winding barrel to be received therein so that the webbing does not lie about in the cabin. Furthermore, generally, the webbing retractor is provided therein with an inertia lock mechanism for preventing the webbing form being wound off only in an emergency of the vehicle, so that the occupant can freely move his body during normal running condition of the vehicle.
However, since the biasing force for winding up the webbing tends to give the occupant a feeling of being repressed, said biasing force cannot be further increased, and is set to the minimum level required for winding up the necessary length of the webbing after the webbing is unfastened from the occupant. For this reason, only a very weak biasing force for winding up the webbing is applied to the webbing surroundingly attached to the occupant, whereby considerable clearances are formed between the webbing and occupant and between the occupant and his seat. Consequently, even after the windoff of the webbing is stopped in an emergency of the vehicle, until said clearances are decreased and the webbing is closely attached to the occupant, the occupant is moved in a direction of collision of the vehicle under unsatisfactory restraint.
From this reason, heretofore, there has been proposed a webbing retractor provided therein with a so-called preload mechanism in which a sudden windup force is applied to the webbing in an emergency of the vehicle to secure the occupant to his seat. However, said preload mechanisms have presented drawbacks such as difficulties in clearly distinguishing it from the webbing windup mechanism during normal running of the vehicle, which contributes to cause a malfunction, troubles hindering normal operations of winding up and off the webbing, unsatisfactory instantaneous windup of the webbing in an emergency of the vehicle, and the like.